As a drill bit button insert that is attached to a button inserts mounted in a drill bit and that performs a drilling, there is disclosed a drill bit button insert in which an abrasive layer formed of a sintered body of polycrystalline diamond which is harder than a tip body is coated on the button insert working/cutting surface of the tip body formed of a cemented carbide. Here, in U.S. Pat. Nos. 4,694,918, 8,573,330, 8,695,733, 8,292,006 and Japanese Patent No. 4676700, drill bit button inserts formed of an abrasive layer as a multilayer structure are mainly proposed for relieving stress in the polycrystalline diamond sintered body. The multilayer structure has a slope so that hardness is decreased and toughness is increased from the outermost layer on the surface of the abrasive layer toward the tip body side.
Generally, the outermost layer of such an abrasive layer of the multilayer structure is a polycrystalline diamond sintered body of a composition sintered by adding Co or the like as a metal binder (metal catalyst) to diamond particles. In addition, in an inner layer, the content of diamond is decreased and metal carbide such as WC is added instead, so that the toughness is enhanced, while maintaining higher hardness than the tip body. It is proposed that the inner layer has a further multilayer structure, and as closed to the inner layer, the diamond content is decreased and the WC content is increased to give the slope in hardness and toughness.